Fastener

ABSTRACT

A fastener has a body and a cage with cam surfaces formed on interengaging components to inhibit relative rotation. A washer is interposed between said surfaces and has oppositely directed faces with cam surfaces formed on one face and serrations on the other. The serrations engage the planar underside of the body.

This application is a continuation of PCT Application No. PCT/CA03/00769 filed on May 30, 2003, which claims priority from U.S. application Ser. No. 10/157,895 filed on May 31, 2002.

The present invention relates to fasteners.

It is well known to use threaded fasteners to secure components to one another. It is also well known to inhibit separation of the fasteners by providing a vibration resistant washer between the fastener and the component. Typically this would take the form of a spring washer inserted between a face of a nut and a component being clamped.

An alternative form of fastener is shown in U.S. Pat. No. 5,626,449 to Hong Kong Disc Lock Company. In this type of fastener a washer is inserted between the nut and the component and opposed faces of the nut and washer are provided with cam surfaces. The cam surfaces effect axial movement between the washer and the nut upon relative rotation. By arranging for the cam surfaces to have an angle greater than the helix angle of the thread of the nut, unintentional removal of the nut is avoided.

An arrangement shown in U.S. Pat. No. 5,203,656 utilizes a pair of cam surfaces by the provision of an intermediate member between a lower washer and a nut. This is referred to as a three-piece arrangement. However, a disadvantage of the arrangement shown in '656 patent is that a central pilot is used to retain the intermediate component on the nut. The pilot is swaged in situ which leads not only to expensive manufacture but also requires close control of the tolerances to ensure the necessary rotational and axial clearances are provided.

U.S. Pat. No. 5,688,091 to McKinlay discloses a similar type of fastener to that of U.S. Pat. No. 5,626,449 in which a cage is used to retain a washer beneath the flared head of a nut. In this arrangement however a cam is provided between the nut and washer. The face between the washer and the cage is planar to provide a single pair of cam surfaces between the washer and nut. The adjacent planar surfaces between the washer and cage allow the washer to rotate as it is tightened. However, it has been found that this arrangement will rotate due to vibration to undo the fastener in the majority of applications.

In PCT application CA99/00985, a number of arrangements of fasteners are shown that offer enhanced performance over these prior fasteners. Whilst excellent performance has been demonstrated with such fasteners, it is found that in applications where there is the possibility of repeated use, the cam faces formed on the underside of the body of the nut may not withstand repeated tightening. Industry standards require the nut body to be relatively soft and the hardened cams on the engaging washer tend to damage the cams on the nut with repeated use.

It is an object to the present invention to obviate or mitigate the above disadvantages.

In general terms the present invention provides a fastener which has a body with an end face and a cage rotatably secured to the body with a planar face directed toward the end face. The sidewalls of the cage extend toward and over the lower portion of the body to permit rotation but inhibit axial separation. A pair of washers is interposed between the body and the cage and has a pair of oppositely directed faces to overlie respective faces on the body and cage. Opposed pairs of faces are provided with complimentary cam surfaces so that relative rotation between the components of the fastener cause axial displacement of the components.

Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which:—

FIG. 1 is a perspective view of a fastener.

FIG. 2 is a section through a fastener installed between a pair of components.

FIG. 3 is an enlarged view of a portion of the fastener shown in FIG. 1.

FIG. 4 is a view on the line IV-IV of FIG. 3.

FIG. 5 is a plan view on the line V-V of FIG. 3.

FIG. 6 is an exploded view of the components in an alternative embodiment of fastener.

FIG. 7 is a view on an enlarged scale on the line VI-VI of FIG. 6,

FIG. 8 is a section of a further embodiment fastener.

FIG. 9 is a plan view of FIG. 8 with portions thereof sectioned for clarity.

FIG. 10 is a section through a tool used to form the embodiment of FIG. 9.

In reference to FIGS. 1 and 2, a fastener generally indicated 10 includes a bolt 12 having a head 14. The bolt 12 includes a threaded shank 16 on which is threaded a nut assembly 18.

The nut assembly includes a body of 20 having planar flats 22, typically arranged as sides of a hexagon, and an internal bore 24 having a thread form corresponding to the shank 16.

The lower end of the body 20 is flared to provide a skirt 26 with a generally planar end face 28. Upper surface 29 of skirt 26 intersects the flats 22 at a raduissed fillet 31 whose height alternates between high and low from flat to flat.

A cage 30 is positioned adjacent the end face 28 and has a bottom wall 32. The bottom wall 32 has an inwardly directed face 33 spaced from the end face 28. A central aperture 35 is provided to receive the bolt 12. A peripheral sidewall 34 extends axially toward and beyond the flared skirt 26.

The cage 30 is heat treated to provide two zones of different physical characteristics with the bottom wall 32 relatively hard and the sidewall 34 more ductile. The upper extremity of the sidewall 34 is locally deformed radially inward to overlie the sloped upper surface of the skirt 26 and limit relative axial movement between the cage 30 and the body 20. The local deformation which is facilitated by the ductility of the sidewall, is provided at six uniformly spaced locations indicated at 37 that provide circumferential abutments as well as radial retention between the cage 30 and body 20.

A pair of washers 36, 37 are interposed between the cage 30 and body 20. Each of the washers 36, 37 has a pair of oppositely directed end faces, 38, 40 and 39, 41 respectively. As can best be seen in FIG. 3, the opposed faces 38, 41 of the washers 36, 37 respectively are formed with complimentary cam surfaces 42, 42′. The cam surfaces 42, 42′ each includes a series of planar facets 46 inclined to a radial plane and uniformly distributed about the longitudinal axis of the bolt 12. The facets 46 are parallel to one another to provide full face contact. The facets 46 are interconnected by a generally axially extending risers 48 to provide pairs of opposed toothed surfaces that are parallel to one another. The inclination of the facets 46 is selected to be greater than the helix angle of the thread form 24 so that the axial movement induced by cooperation of the surfaces for a given rotation of the body relative to the fastener is greater than the axial displacement of the body 20 relative to the shank 16. The aggregate height of the risers 48 for each set of cam surfaces 42, 42′ is typically the 1.5 times pitch of the thread to achieve satisfactory locking. The height of each risers 48 is determined by dividing the aggregate height by the number of facets. The number of facets is selected to be an integral multiple of the number of flats and, for the cam surfaces 42, 42′ 12 facets is found satisfactory. The height of the risers 48 will then be 1.5 times the pitch divided by 12.

Complementary cam surfaces 44, 44 ¹ are formed on opposed faces 40, 33 of the washer 36 and bottom wall 32, respectively. The cam faces, 44, 44′ also includes a series of parallel planar facets 50 similar to facets 46 of cam surface 42 but oppositely directed with respect to facets 46. The number of facets 50 is greater than the facets 46, but the aggregate height of risers 52 that interconnect the facets 50 is similar. Accordingly, the height of each of the risers 52 is less than that of risers 48. The cam surfaces 42, 42′ are therefore relatively coarse and the cam surfaces 44, 44′ relatively fine. Cam surfaces 44 will cooperate when subject to vibration to inhibit relative rotation between the cage 30 and washer 36. This allows the cams 42 to cooperate and prevent loosening of the nut 17.

In a typical embodiment, the 360° circle of coarse and fine cams will each have a total number divisible by the wrenching flats of the nut. For a hexagonal nut therefore, the coarse cam circle will typically consist of twelve cams, for diameters from ½ to 1-{fraction (1/2)} inches inclusive and the fine cam circle will consist of 18 cams.

The radial extent of the cams measured from the inner edge of the bore will range from 5 mm to 8 mm depending on the bolt diameter.

The face 39 of washer 37 is formed with a series of fine serrations, 55 extending radially and disposed uniformly around the circumference of the face 39. The serrations 55 have inclined surfaces 56 that are angled at approximately 15° with respect to the radial plane of the washer 37 and terminate in axial faces having an axial length in order of 0.20 mm to 0.25 mm. In a typical washer used with a M20 nut (20 mm nominal bolt diameter) the washer 37 will have a diameter of 38 mm and there will be 84 serrations extending about the face 39. For a M22 nut, the number of serrations is increased of 90. It is found that the depth of the serrations is not as critical as the included angle between the inclined and axial faces 56, 57 where the 15° shape provided the requisite sharpness at the extremity of the serrations. The serrations 55 are directed oppositely to the facets 46 (i.e. the axial faces 57 face the same directions as the risers 48 when on oppositely directed faces) and engage the planer undersurface 28 of the body 20 and inhibit rotation between the washer 37 and body 20 in one direction. The body 20 typically has a hardness between 28 and 36 Rockwell C and the washers 36, 37 have a hardness of between 45 and 48. The serrations 55 are thus able to penetrate the under surface 28 upon axial loads being imposed.

The nut assembly 18 is preassembled by inserting the washers 36, 37 into the cage 30 and the body 20 placed on the washer 37. The sidewalls 34 are then radially displaced to overlap the upper surface 29 of flared skirt 26. The ductility of the sidewalls facilitates the displacement while permitting lower face to retain the hardened bearing surface. Preferably, the number of locations where the sidewalls are radially displaced will be similar to the number of wrenching flats on the nut although this may be varied to be either greater or lesser depending on circumstances. Limited axial displacement is provided between the cage 30 and the body 20 allowing the cage 30 to rotate relative to body 20. It has been found that the greater height and added hoop strength available at the nut flange provides 30% more strength than a standard nut.

To fasten a pair of components indicated (A) and (B) in FIG. 2, the bolt 12 is passed through an aligned aperture in the two components and the nut assembly 18 threaded onto the shank 16. As the lower face of the cage 30 engages the upper surface of component (A), the cam surfaces 42, 42′ and 44, 44′ are brought into engagement and the serrations 55 engage the underside 28 of the body 20. The washers 36, cage 30 and body 20 are rotated conjointly. The risers 48 provide torque transmission between the washers 36, 37 and facets 46 between washer 36 and cage 30.

The nut assembly 18 is tightened to the requisite torque to hold the two components (A) and (B) with a wrench in a conventional manner.

In use, if the bolt 12 extends due to the axial loads placed upon it, relative rotation between cage 30 and body 20 will cause the ridges 48 to engage and the facets 46 of opposed faces to slide across one another. The washer 37 is carried with the body 20 by the virtue of the engagement of the serrations 55 with the undersurface 28 to cause relative rotation between cam surfaces 42,42. This induces an axial displacement between the faces, which is greater than the axial displacement provided by a corresponding rotation of the body 20 on the shank 16. As such a binding or interference is provided between the components and an unintentional separation is inhibited.

To remove the nut assembly 18, sufficient torque is applied to rotate the nut and cup conjointly and release the tension in the bolt.

During tightening, the serrations 55 engage the underside 28 of body 20 and transmit the torque through the washers 36, 37. However, the serrations 55 do not cause significant damage to the undersurface 28. The separate washer 37 permits the cams 42 to be formed from a harder material and therefore ensure that they retain their functionality for repeated applications.

It will be appreciated that this arrangement may also be incorporated into a nut in which the body 20 is formed with a conical protrusion for centering the fastener on a workpiece.

The arrangement depicted in FIGS. 1 to 5 is referred to as a four-piece arrangement because it includes the nut 17, two washers 36, 37 and cage 30. A three-piece arrangement may also be produced, as shown in FIGS. 6 and 7 wherein the washer 36 is eliminated so that the cam surface 42 of the washer 37 and the cam surface 44 on inside bottom surface of the cage 30 engage. Each are produced with oppositely directed coarse cams which are complementary to each other.

In this case, the cage 30 c has fine serrations 55′c, angled at 15° with respect to a radial plane on the outside bottom of the cage 30 c. The serrations 55′c are directed oppositely to the facets 46 c that are located on the inside bottom of the cage 30 c. The serrations 55′c engage with the workpiece (A) and stop the cage 30 c from moving. Similarly, the serration 55 c engage the undersurface 28 of the body 20 to inhibit relative rotation between the body 20 and washer 37. Accordingly, when subject to vibration, the coarse cams move up the incline and lock the nut 17.

In each of the above embodiments a hexagonal body has been illustrated but it will be recognized that other forms of nut may be used such as barrel nuts with longitudinal grooves or other commonly available forms. It will also be appreciated that the fastener 10 may be incorporated in to the head of a bolt rather than a nut with the underside of the head serving as the undersurface 28 and the cage extending about the head. Such an arrangement may be used with conventional hexagonal heads or other forms such as socket or domed headed bolts.

The nut assemblies of FIGS. 1 through 5 or 6 and 7 may also be used advantageously with studs secured in a blind hole and is particularly beneficial when used with a tension control splined tip.

In certain configurations it has been found that there is sufficient elasticity in the threaded shank 16 to allow the nut 18 to be undone by driving it over the facets 46. To avoid this a further embodiment is shown in FIGS. 8 and 9 of a fastener having either a three-piece arrangement similar to that shown in PCT application CA99/00985 (i.e. with the washer 37 and serrations 55 omitted) or with a configuration as shown in FIGS. 1 to 5. Like reference numerals will be used to identify like components with a suffix “h” added for clarity. In the embodiment shown in FIG. 8, the peripheral sidewall 34 h of the cage 30 h is formed with a lower cylindrical portion 94 and an upper frustoconical portion 96. A circlip 90 is located within the cage 30 h between the upper inclined surface 29 h of flared skirt 26 h and the inwardly directed inclined surface 98 of frusto-conical portion 96. Circlip 90 is typically a flat band, having a “C” configuration to allow flexure to reduce the diameter of the circlip 90.

Circlip 90 is dimensioned to limit the axial displacement available between cage 30 h and body 20 h of nut assembly 18 h. As can be seen in FIG. 7, the circlip 90 is positioned adjacent the transition between the portions 94,96 of the sidewall 34 h so that relative axial movement of the body 20 h away from bottom wall 32 h will attempt to reduce the diameter of the circlip 90. The fastener 10 h is assembled by inserting washer 36 h into cage 30 h, the body 20 h then being placed on washer 36. In the preferred assemblage, circlip 90 is then placed on body 20 h and the sidewall 34 h of cage 30 h is then radially inwardly displaced to overlap the upper surface 29 h of flared skirt 26 h.

In the alternative, circlip 90 may be introduced into cage 30 h after the sidewalls 34 h have been radially displaced. In this case, on assembly of the fastener, the ends of circlip 90 are compressed toward one another decreasing the radius of the circlip for installation within cage 30 h. When the ends are released, circlip 90 expands with the tensioned band returning to the original configuration, and is retained within cage 30 h.

Upon application of a reverse torque to the fastener 10 h, opposed camming surfaces provided by the facets 46 h of washer 36 h and end face 28 h of body 20 h slide relative to one another as described in FIG. 3 to induce a relative axial displacement. The upper surface 29 h engages with the circlip 90 to limit the axial displacement and thereby relative rotation. Further rotation requires displacement of the circlip 90 relative to the cage 34 h which is inhibited by the compressive and friction forces. The conical portion 96 requires a progressive compression of the circlip 90, as it is axially displaced, thereby presenting a progressively increasing force. The circlip 90 provides an abutment that limits the axial displacement to a height less than that of the ridge 48 h. The force required to cause further elongation of the shank 16 h is thus dramatically increased to inhibit removal of the nut assembly 18 h. In the preferred embodiment the allowable axial displacement is limited by the circlip 90 to one fourth the height of the ridges 48 h.

The circlip 90 is intended to prevent the removal of the fastener once installed. In the event, that removal of the fastener is desired, circlip 90 is removed from the cage 30 h by circlip pliers, and the fastener 10 h is removed as previously described. Upon reassembly, the circlip 90 may be replaced or, preferably a new nut assembly is utilised.

A two-piece fastener arrangement may also be produced, though not shown, wherein washer 36 is eliminated such that the cam surface 42 of nut 17 and cam surface 44 on the inside bottom surface of cage 30 engage. Each of these cam surfaces is produced with oppositely directed course cams which are complementary to one another. The circlip 90 is located between the cage 30 and flared skirt 26 as described above. The provision of circlip 90 causes body 20 and washer 26 to remain in a substantially fixed relationship within cage 30 as circlip 90 limits the potential axial displacement of same. If required, the serration's may be provided on the lower face of the cage as described with reference to FIGS. 5 and 6.

The nut assembly 18 detailed in FIG. 17 has frusto conical upper portions 96 of sidewalls 34 h which may be formed using the tool 100 shown in FIG. 9. The tool 100 includes a cylindrical barrel 102 with an internal cavity 104. The cavity 104 is formed by three counterbores 106,108,110. The counterbores 106,108,110 are arranged in a step-like and interconnected by radiussed fillet 112, 114 respectively. The outermost bore 106 is dimensioned to correspond to the diameter of the lower cylindrical portion 94 of cage 30 so that the undeformed peripheral wall 34 is a snug fit within the counterbore. The counterbores 108,110 are adapted to receive the nut 22 and shank 16 respectively in a freely fitting manner.

To radially displace the sidewalls 34 h of cage 30 h and form the frusto-conical portion 96, tool 100 is placed over the top outer edges of cage 30 h so as to receive the peripheral portion in the counterbore 106 with the washer 36 h, body 20 h and circlip 90 located within the cage 30 h. On application of downward force on tool 100, the upper edge of the sidewall 34 h is forced into the radiused fillet 112 and deflected inwardly in a uniform manner. This uniform application of force by tool 100 avoids the formation of local deformations as in the previously described embodiments, and enables a continuous fold in the cage material.

Tool 100 may be used in combination with fasteners having a variety of different diameters and the radius adjusted to provide the required deflection.

It will be seen therefore that a simple yet effective fastener has been described that provides the requisite resistance to vibration and at the same time is relatively easy to manufacture. 

1) A fastener comprising a body having a planar end face, a cage rotatably secured to said body and having a radial face directed toward said end face and side walls extending toward and overlying a portion of said body to inhibit axial separation, and a washer interposed between said body and said cage, said washer having a pair of oppositely directed faces, one of said faces being directed toward said planar end face of said body and having serrations formed thereon for engagement with said planar end face to inhibit relative rotation therebetween, and the other of said faces being directed toward said radial face of said cage and having a cam surface formed thereon, said cam surface engaging a complementary cam surface on an oppositely directed face to induce relative axial movement upon rotation between said faces. 2) A fastener according to claim 1 wherein said complementary cam surface is formed on said radial face of said cage. 3) A fastener according to claim 2 wherein said cage has an outer surface oppositely directed to said radial face and serrations are formed on said outer surface. 4) A fastener according to claim 1 wherein said complementary cam surface is formed on a second washer interposed between said radial face and said other of said faces. 5) A fastener according to claim 4 wherein said radial face and said second washer have opposed faces and a second set of complementary cam surfaces are formed on said opposed surfaces to induce axial displacement upon relative rotation therebetween. 6) A fastener according to claims 1 wherein said body has a flared skirt adjacent said radial face and said side walls overlap said skirt. 7) A fastener according to claim 6 wherein said body is a nut having planar flanks to permit torque transmission thereto. 8) A fastener according to claims 1 wherein each of said cam surfaces include a plurality of inclined facets distributed about an axis of rotation. 9) A fastener according to claim 8 wherein said facets are interconnected by ridges to provide a torque-transmitting abutment between said faces. 10) A fastener according to claim 5 wherein said cam surfaces on opposite sides of said second washer are different. 11) A fastener according to claim 10 wherein said facets associated with one of said cam surfaces are inclined of different length to facets associated with the other of said cam surfaces. 12) A fastener according to claim 10 wherein said body has a plurality of flats formed thereon to define a polygonal body and the number of said facets is an integral multiple of the number of flats. 13) A fastener according to claim 1 wherein said serrations are asymmetric and extend substantially continuously across said surface, each of said serrations having an inclined facet and a generally axial end face and being oppositely directed to said cam surface. 14) A fastener according to claim 13 wherein said facets are disposed at 15° to a radial plane. 15) A fastener comprising a body having an end face, a cage rotatably secured to said body and having a radial face directed toward said end face and side walls extending toward and overlying a portion of said body, said radial face and said end face being interconnected by cam surfaces formed thereon and operable to induce relative axial movement upon relative rotation between said faces, and an abutment between said cage and said body to limit axial separation therebetween. 16) A fastener according to claim 15 wherein said abutment is selectively removable to permit increased axial movement between said body and cage. 17) A fastener according to claim 15 wherein a washer is interposed between said body and said cage, said washer having a pair of oppositely directed faces, one of which is directed toward said end face of said body and the other of which is directed toward said radial face of said cage, opposed faces of said fastener having complementary cam surfaces thereon to induce relative axial movement between said body and said cage. 18) A fastener according to claim 17 wherein said abutment is selectively removable to permit increased axial movement between said body and cage. 19) A fastener according to claim 18 wherein said abutment is resilient to facilitate insertion between said cage and said body. 20) A fastener according to claim 19 wherein said cage has an inclined wall extending across but spaced from said body and said abutment is removably secured between said inclined wall and said body. 21) A fastener according to claim 20 wherein said body has a flared skirt and said side walls overlap said skirt. 22) A fastener according to claim 21 wherein said flared skirt is surmounted by a nut having planar flanks to permit torque transmission thereto. 23) A fastener according to claim 22 wherein said complementary cam surfaces include a plurality of facets inclined to a radial plane and interconnected by ridges to provide a torque-transmitting abutment between said faces. 24) A fastener according to claim 22 wherein said cam surfaces associated with respective ones of said opposed pairs of faces are different. 25) A fastener assembly for securing a pair of components to one another, said fastener assembly including a bolt having a head with a first end face directed toward one of said components and a threaded shank depending from said head, a nut having a body and a second end face directed toward another of said components, said body being threaded to receive said shank, a cage secured to one of said head and said body and having a radial face extending across a respective one of said end faces, an abutment acting between said cage and said body to limit relative axial movement therebetween and a washer interposed between said cage and said end face, said washer having a pair of oppositely directed faces, one of which is directed toward said one end face and the other of which is directed toward said radial face of said cage, opposed pairs of said faces having complementary cam surfaces formed thereon to induce axial movement upon relative rotation between said faces. 26) A fastener according to claim 25 wherein said abutment is selectively removable to permit increased axial movement between said body and cage. 27) A fastener according to claim 26 wherein a washer is interposed between said body and said cage, said washer having a pair of oppositely directed faces, one of which is directed toward said end face of said body and the other of which is directed toward said radial face of said cage, opposed faces of said fastener having complementary cam surfaces thereon to induce relative axial movement between said body and said cage. 28) A fastener according to claim 27 wherein said abutment is selectively removable to permit increased axial movement between said body and cage. 29) A fastener according to claim 28 wherein said abutment is resilient to facilitate insertion between said cage and said body. 30) A fastener according to claim 29 wherein said cage has an inclined wall extending across but spaced from said body and said abutment is removably secured between said inclined wall and said body. 31) A fastener according to claim 30 wherein said body has a flared skirt and said side walls overlap said skirt. 32) A fastener according to claim 31 wherein said flared skirt is surmounted by a nut having planar flanks to permit torque transmission thereto. 33) A fastener according to claim 30 wherein said complementary cam surfaces include a plurality of facets inclined to a radial plane and interconnected by ridges to provide a torque-transmitting abutment between said faces. 34) A fastener according to claim 33 wherein said cam surfaces associated with respective ones of said opposed pairs of faces are different. 